Agents

Not much is known about what it means to be an agent. The agent's headquarters is in Dubai and, in order to enter, one must have a "seal" on their body. The seals that mark Naito and Yuta's chest is what allows them access. Arthur has a seal on his forearm that is typically covered by the sleeve of his jacket[1]. It would also appear that Naito and Yuta's father was an agent as well[2].